Relationship between grain size and the degrees of orientation in a twinned ErBa 2 Cu 3 O y superconductor oriented in m
- PDF / 29,590,714 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 50 Downloads / 125 Views
Relationship between grain size and the degrees of orientation in a twinned ErBa2Cu3Oy superconductor oriented in modulated rotating magnetic fields Shigeru Horii1, Shota Okuhira1, Momoko Yamaki1, Masakazu Haruta1 and Jun-ichi Shimoyama2 1 Department of Environmental Systems Engineering, Kochi University of Technology, Kami-shi, Kochi 782-8502, Japan 2 Depatment of Applied Chemistry, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656, Japan ABSTRACT We report the dependences of the degrees of tri- or bi-axial orientation on strength of applied magnetic fields of modulated rotating field (MRF) for twinned ErBa2Cu3Oy (Er123) powder samples oriented in epoxy resin under various MRF conditions. Introduction of a pulverization process in the Er123 powders improved the degrees of inplane orientations, and is effective for enhancing the inplane magnetic anisotropy of Er123 grains with twin microstructure. Formation of inhomogeneous domain structure is a dominant factor of the enhancement, and the present study indicates possibility of tri- or bi-axial orientation of the twinned Er123 grains even under relatively low MRF conditions around 1 T. INTRODUCTION Recent improvement of magnetic alignment techniques enabled simultaneous alignment of both the easy and hard axes of magnetization, tri-axial orientation, by using a modulated rotating magnetic field (MRF)[1]. Applying this tri-axial magnetic orientation requires substances having grain level tri-axial magnetic anisotropy. At the current stage, due to the development of 10 T class of cryogen-free superconducting magnets[2], magnetic orientation of feeble magnetic materials with diamagnetism and paramagnetism has been reported[3,4], and, in practice, tri-axial orientation of feeble magnetic materials has been also achieved as proof-ofprinciple[1, 5, 6]. One of issues for practical use of high-critical-temperature (high-Tc) cuprate superconductors is the formation of tri-axial oriented microstructure due to the layered crystal structure with two dimensional superconducting CuO2 plane and the d-wave symmetry of the Cooper pairs[7]. In the case of REBa2Cu3Oy (RE123) compounds with Tc ~ 90 K, epitaxial thinfilm-growth[8] on highly oriented substrates and melt-solidification with seed crystals[9] are used. Because magnetic alignment is a room-temperature process, tri-axial magnetic alignment technique using MRF will be extensively applied for high-Tc cuprate superconductors having magnetic anisotropy along each crystallographic axis with sufficiently large differences in magnetization for the improvement of critical current properties as well as for polycrystalline superconductors. However, because of introduction of twin microstructure[10] into the RE123 grain in the ab-plane due to the tetragonal-orthorhombic transition induced by its nonstoichiometric oxygen content, inplane magnetic anisotropy of the RE123 grains is reduced and tri-axial magnetic alignment is probably hard to achieve in RE123.
Figure 1. Schematic diagram of the relationship among Ha, measured
